JPH0112809B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention is a method for desiliconization and dephosphorization that is applied to hot metal that has not been substantially pretreated (including undesilicated hot metal and lightly desiliconized hot metal; the same applies hereinafter). The present invention relates to a treatment method, and particularly to a method that can efficiently carry out desiliconization and dephosphorization reactions within a short period of time. [Prior art] Pre-treatment of hot metal is carried out with the main purposes of desiliconization, dephosphorization, and desulfurization. A system is being perfected that removes impurities and allows the converter to exclusively decarburize and raise the temperature of the molten steel. By the way, in recent years, research has progressed to improve the desiliconization method in blast furnace casthouses, and a method in which desiliconization is performed during the tapping process from the tap runner and then dephosphorization and desulfurization in the pretreatment furnace has become widely used. When carrying out desiliconization of the blast furnace cast bed gutter, the wear and tear of the cast bed gutter becomes significant, requiring considerable effort and expense to maintain and manage it, as well as loss of valuable elements (Fe and Mn) and a drop in hot metal temperature. It becomes an amount that cannot be ignored. Under these circumstances, the present invention targets hot metal that has not been substantially subjected to pretreatment (including cases where it has been lightly desiliconized; the same applies hereinafter), and the present invention aims to provide hot metal that has not been subjected to any preliminary treatment (including cases where it has been lightly desiliconized; the same shall apply hereinafter). The present invention aims to provide a method that can improve the processing efficiency in a pretreatment furnace in a method for desiliconization and dephosphorization in a treatment furnace. As a method for desiliconization and dephosphorization in a pretreatment furnace, for example, as disclosed in JP-A-58-16006, a flux powder consisting of CaO, iron oxide, and a solvent (reaction accelerator if necessary) is heated in a carrier gas. There is a method of promoting desiliconization and dephosphorization using a combination of blowing into the deep part of hot metal (hereinafter simply referred to as injection) and top blowing with oxygen, and it is also possible to perform desulfurization treatment subsequently. [Problems to be Solved by the Invention] However, the flux used in the above method is all in powder form, and all of this is supplied by the injection method, so the manufacturing cost of the flux itself is high. In addition, especially when applied to hot metal with a high silicon content that has not been subjected to preliminary desiliconization treatment, a considerably large amount of flux must be input due to the need to adjust the slag basicity, which further increases costs. There is a problem involved. In addition, if a large amount of flux is to be injected, it is theoretically unavoidable that the total treatment time will increase, and as a result, decarburization in the hot metal will proceed faster than planned, and the heat-raising effect during converter operation will increase. This creates a new problem of having to struggle with heat compensation in the converter. On the other hand, there is a considerable difference in the reaction mechanism between the desiliconization reaction and the dephosphorization reaction in hot metal, and it has been confirmed that the desiliconization reaction in particular progresses rapidly at the initial stage, determined by the rate of oxygen supply. Regarding the phosphorus reaction, after the amount of Si in the hot metal decreases to a certain level (approximately 0.10%), the phosphorus in the hot metal is captured by the dephosphorization flux on the surface of the hot metal or by the dephosphorization flux floating in the hot metal, and the reaction rate increases. It has also been confirmed that there is an increase in However, in conventional desiliconization and dephosphorization methods that use a pretreatment furnace, including the above-mentioned method, the desiliconization and dephosphorization methods described above
It cannot be said that treatment methods are adopted that fully take into account the differences in the dephosphorization mechanism, and as a result, it takes a long time to desiliconize and dephosphorize (as a result, the hot metal temperature decreases or C and
(resulting in a decrease in Mn, etc.) and consuming a large amount of flux. The present invention has been made with attention to these circumstances, and even when applied to hot metal with a high Si content that has not been substantially subjected to desiliconization treatment, the above-mentioned disadvantages do not occur, and the total amount of flux used can be reduced. This reduces costs and contributes to lower costs.
It also aims to establish a new desiliconization and dephosphorization method that can shorten the total processing time required for desiliconization and dephosphorization and suppress decarburization. [Means for Solving the Problems] The present invention that achieves the above object has the following gist. In other words, hot metal that has not been substantially subjected to desiliconization treatment (0.2%≦Si concentration≦0.5%)
The hot metal is charged into a pretreatment furnace, and the surface of the hot metal in the pretreatment furnace is covered with dephosphorization flux, and the hot metal is dephosphorized by adding oxygen top-blowing and injection of desiliconization flux containing an oxygen source for desiliconization. In carrying out desiliconization/dephosphorization, during the desiliconization reaction promotion period, top blowing is performed so that the desiliconization oxygen supply rate [V ₀ (unit: Kg/1 ton/min of hot metal)] satisfies the following equation [ ]. Desiliconization and dephosphorization are carried out by adjusting the oxygen blowing conditions and/or the injection conditions of the desiliconizing flux. [V ₀ ] = η _s・O _s + η _g・O _g ≧ 2 [Si] ₀ −0.2 … [] However, [Si] ₀ : Silicon concentration in hot metal before treatment (wt%) η _g : Top-blown oxygen Desiliconizing oxygen efficiency (10 ^-2 %) 0.2≦η _g ≦0.7 η _s : Desiliconizing oxygen efficiency of desiliconizing flux (10 ^-2
%) 0.4≦η _s ≦1.0 O _g : Top-blown oxygen supply rate (Kg/t・min) O _s : Injection rate of desiliconization flux (oxygen content equivalent value: Kg/t・min) [Effect] The above technical As revealed by the means,
The first feature of the present invention is that the flux injection is not carried out alone, but is combined with the top addition of dephosphorizing flux (a technique of coating and placing dephosphorizing flux on the surface of hot metal; the same applies hereinafter). exists, and the desiliconization reaction is made to proceed rapidly by controlling the desiliconization oxygen supply rate so as to satisfy the relationship of the above formula [] during the desiliconization reaction acceleration period at the beginning of the process, and thereafter the oxygen supply rate is The second feature is that the dephosphorization reaction can be carried out efficiently while being suppressed to a low level, and by adopting such a configuration, the above-mentioned problems can be solved at once. The most preferable flux for top addition used in the present invention is one whose main component is CaO,
The CaO is of high purity (like lump lime 98
%) and low-purity products (such as converter slag).
(approximately 50%, etc.) can be used. The latter converter slag contains 1/3 to 1/4 SiO ₂ , so it has the disadvantage that the amount used is slightly higher, but in addition to lower cost, it improves dephosphorization efficiency due to the increase in slag T and Fe. This is advantageous in terms of improving the CaO selected as the main component is a useful component as a dephosphorizing agent, and the present invention aims at strengthening the dephosphorizing effect by adding flux at the top. Incidentally, since the desiliconization effect by CaO is also exhibited in parallel, the hot metal pretreatment effect according to the present invention has a remarkable effect not only in dephosphorization but also in desiliconization. However, CaO has the disadvantage of having a high melting point and lack of slag forming property, so it is not used as a material for improving slag forming property.
Low melting point components such as Mn ore and calcium fluoride are used together. That is, the flux added to the top (dephosphorization flux) used in the present invention is mainly composed of CaO and a slag slag improving material, and the cooperative action of these forms a highly fluid slag, Coupled with the effect of increasing oxygen potential due to blown oxygen, various reactions such as dephosphorization at the slag-metal interface are promoted. Judging from the viewpoint of promoting the dephosphorization reaction, the lower the interfacial temperature mentioned above, the better the results, so it is also effective to mix mill scale or iron ore into the above flux as a coolant, which lowers the melting point of the slag. It can also be expected to contribute to dephosphorization by promoting the reaction between slag metals and improving the oxygen potential in the slag.
Moreover, since CaO has the function of promoting not only the dephosphorization reaction but also the desiliconization reaction, it can effectively proceed with the desiliconization and dephosphorization of hot metal in conjunction with the injection of desiliconization flux described below. Next is the desiliconization flux.As mentioned above, the desiliconization reaction progresses rapidly depending on the rate of oxygen supply, so the main component is iron oxide (including mill scale and iron ore, the same applies hereinafter), which has a high oxygen supply ability. The one that does is the best. When the desiliconization flux is formulated with only iron oxide, it is not necessary to incorporate a slag-improving agent such as _CaF2 , but if the flux for injecting is expected to have a dephosphorizing effect, it may be necessary to add it to the flux.
CaO can also be blended, and in such cases, it is recommended to blend some slag accelerator. Si and P during desiliconization and dephosphorization of hot metal
If we examine the details of the decline in
As shown in the figure, the desiliconization reaction first progresses rapidly and most of the Si is removed, and then the dephosphorization reaction progresses. Therefore, the desiliconization reaction must proceed promptly. To achieve this, considering that the desiliconization reaction initially progresses at a rate limited by oxygen supply, we believe that it would be best to inject a large amount of desiliconization flux from the initial stage of the pretreatment and to increase the top-blown oxygen supply rate. In fact, desiliconization progresses rapidly through such treatment. However, if these treatment conditions are continued as they are, a problem arises in that the decarburization and deMn reactions become significant. Therefore, the inventors of the present invention solved these problems, and not only completed desiliconization in the shortest possible time, but also rapidly proceeded with the subsequent dephosphorization reaction, and also achieved decarburization and deMn removal.
In order to suppress reactions to the minimum, we thought that it would be necessary to separate the above pretreatment into a desiliconization reaction promotion period and a dephosphorization reaction period and determine appropriate stirring conditions.
Further research was carried out by introducing the concept of desiliconization oxygen supply rate shown in the above formula [ ]. As a result, if the blowing conditions of top-blown oxygen and/or the injection conditions of the desiliconizing flux are adjusted so that the desiliconizing oxygen supply rate during the desiliconizing reaction promotion period at the beginning of the process satisfies the relationship of the above formula [], It was found that the above problem was successfully solved. That is, as mentioned above, the initial desiliconization reaction proceeds with the rate of oxygen supply, and the oxygen consumption [O ₂ ] in the promotion period can be expressed by the following [ ]. [O ₂ ] = {([Si] ₀ − [Si] ₁ ) × 1000 × (1/100)} × (M ₀₂ /M _si ) = {([Si] ₀ − [Si] ₁ ) × 10} × (32/28.1) = 11.4 ([Si] ₀ - [Si] ₁ ) [Kg/1 ton of hot metal: same below]... [] However, [Si] ₀ : Initial amount of Si in hot metal (wt%) [Si ] ₁ : Amount of Si in the hot metal (wt%) at the end of the desiliconization reaction acceleration stage M ₀₂ : Molecular weight of O ₂ M _si : Molecular weight of Si If the amount of Si is 0.10% by weight (the dephosphorization reaction starts to progress rapidly when desiliconization reaches this amount of Si), the following equation [ ] is derived from the above equation [ ]. [O ₂ ] = 11.4 ([Si] ₀ −0.10) = 11.4 [Si] ₀ −1.14 …[] Since the desiliconization rate during the desiliconization reaction promotion period is approximately constant, the desiliconization reaction promotion period was set to 5 minutes. When the desiliconization oxygen supply rate [V ₀ ] to be completed within the above equation is determined based on the above equation, the following equation is established. [V ₀ ] > 1/5 (11.4 [Si] ₀ −1.14) > (2・[Si] ₀ −0.2) …[] The above desiliconization oxygen supply rate [V ₀ ] refers to the top-blown oxygen and desiliconization Of the oxygen supplied from the oxygen source in the flux, it is the oxygen supply rate that is consumed only for the desiliconization reaction (a value excluding the oxygen consumed for the oxidation reaction of C, P, Fe, Mn, etc. in the hot metal). The proportion of oxygen effectively consumed in the desiliconization reaction differs considerably between top-blown oxygen and injected desiliconization flux. Moreover, the above ratio also varies depending on the top-blowing conditions of top-blowing oxygen, the type of desiliconizing flux, injection conditions, etc. _Therefore , in the present invention, in consideration of such fluctuation factors, _coefficients η _g , The requirements of the above formula [] are set so that the sum of the values multiplied by η _s satisfies the relationship of the above formula []. The above coefficient η _g represents the desiliconization oxygen efficiency (10 ^-2 %) of top-blown oxygen, and it was confirmed that it falls within the range of 0.1≦η _g ≦0.5 under normal desiliconization and dephosphorization processing conditions. The coefficient η _s represents the desiliconization oxygen efficiency (10 ^-2 %) of the oxygen source supplied from the injected desiliconization flux, and under normal desiliconization and dephosphorization treatment conditions, 0.2≦η It has been confirmed that _s is within the range of 0.9. As described above, in the present invention, by appropriately setting the desiliconizing oxygen supply rate [V ₀ ] during the desiliconizing reaction promotion period, the desiliconizing reaction can be rapidly advanced.
The transition to the dephosphorization reaction period can be accelerated.
The desiliconization reaction acceleration period in the present invention refers to the period when the amount of Si decreases rapidly at the beginning of the process, as is clear from the above explanation, but as a rough guide,
This can be considered as the period until the Si concentration is reduced to 0.10% or less (the first 3 to 5 minutes in terms of processing time). Next, regarding the dephosphorization reaction period, the dephosphorization reaction takes place mainly at the interface between the upper flux that has turned into slag and the hot metal, and the question is how to effectively move the P component in the lower layer of the hot metal to the hot metal surface without inhibiting the interfacial reaction. This is the most important point in proceeding with the dephosphorization reaction. In other words, during the dephosphorization reaction period, as long as an appropriate stirring force is applied to the hot metal, the dephosphorization reaction can proceed sufficiently by supplying a small amount of top-blown oxygen from the top of the dephosphorization flux. During this period, the oxygen supply rate should be reduced to normal levels to suppress reactions such as decarburization and deMn removal. The time required for dephosphorization depends on the amount of hot metal processed, the shape of the pretreatment furnace, the nozzle structure of the injection lance, the composition and charging amount of the upper dephosphorization flux,
Although it differs slightly depending on the target P concentration, etc., under general conditions, 7 to 10 hours after the desiliconization reaction promotion period has elapsed.
You can consider about a minute as a rough guideline. still in hot metal
The amount of Si has decreased to almost the target level at the end of the desiliconization reaction acceleration period, and the amount of desiliconization that is expected to proceed throughout the dephosphorization reaction period is extremely small, so the transition to the dephosphorization reaction period is The purpose of final desiliconization and dephosphorization can be achieved by simply blowing top-blown oxygen at a normal level toward the upper flux. However, if necessary, a small amount of desiliconizing agent can be injected with a carrier gas. [Example] The upper flux conditions shown below were set, and the desiliconization oxygen supply rate (adjusted by the desiliconization flux composition or top-blown oxygen conditions) was divided into the desiliconization reaction acceleration period and the dephosphorization reaction period as shown in Table 1. As shown, undesilicated hot metal was subjected to desiliconization and dephosphorization treatments with various changes, and changes in each component over time were investigated. <Upper dephosphorization flux (all cases jointly)> Massive quicklime: 6.9Kg/t (1 ton of hot metal: same below) Mn ore: 6.7Kg/t Scale: 8.9Kg/t In addition, stirring of hot metal during the above treatment is as follows: The conditions for blowing the carrier gas were adjusted so that the stirring power value (ε〓) calculated by the following formula was approximately 550 [Watt/1 ton of hot metal] throughout the desiliconization reaction acceleration period and the dephosphorization reaction period. ε〓＝0.0062・Q・Tl／Ml× {ln(1+0.000968ρl・Z) +(1−T ₀ /Tl)} However, Q: Carrier gas flow rate (l/min) Tl: Hot metal temperature (〓) Ml: Hot metal Weight (tons) ρl: Hot metal density (gr/ ^cm3 ) Z: Injection lance immersion depth (cm) _T0 : Carrier gas temperature (〓)

【table】

[Table] The results are shown in Table 2, and can be considered as follows. In the conventional method, the desiliconization oxygen supply rate from both the top-blown oxygen and the desiliconization flux is kept constant throughout the desiliconization reaction promotion period and the desiliconization reaction period, so the desiliconization rate during the desiliconization reaction promotion period is slow, and the effects of this are As a result, the start of the dephosphorization reaction phase is delayed, and it takes a long time to progress the dephosphorization to the target level. On the other hand, Examples 1 to 5 all show examples in which the desiliconization oxygen supply rate [V ₀ ] during the desiliconization reaction promotion period is increased. That is, in Example 1, the supply rate of top-blown oxygen during the desiliconization reaction promotion period was set high, and in Example 2,
In this example, the height of the top blowing lance is lowered during the desiliconization reaction promotion period to increase the desiliconization oxygen supply rate, and in Examples 3 and 4, the amount of scale in the desiliconization flux injected during the desiliconization reaction promotion period is Example 5 is an example in which the desiliconizing oxygen supply rate is increased by increasing the desiliconizing oxygen supply rate, in which the top-blown oxygen supply rate during the desiliconizing reaction promotion period is increased and the amount of scale in the desiliconizing flux is increased to increase the desiliconizing oxygen supply rate. For example, in any case,
As a result of the desiliconization reaction proceeding efficiently during the desiliconization reaction acceleration period of 3 minutes, the phosphorus content decreased to almost the target level during the subsequent seven minutes of desiliconization reaction period. In particular, the desiliconizing oxygen supply rate during the desiliconizing reaction promotion period [V ₀ ]
In Example 5, in which the amount of scale in the desiliconization flux was increased and the top-blown oxygen supply rate was increased, the desiliconization rate during the desiliconization reaction acceleration period was very high, and the final phosphorus concentration was also very low. It is being On the other hand, in the conventional example, the phosphorus concentration after 10 minutes, which is the same as in the example, was extremely high at 0.032%.
Even when the treatment time was extended to 12 minutes, the phosphorus concentration did not decrease to the level of the example, clearly showing the difference from the present invention. Moreover, since the oxygen supply rate during the dephosphorization reaction period is kept low, decarburization reactions and the like are suppressed to the same level as in conventional methods.

[Table] [Effects of the Invention] The present invention is constructed as described above, and by setting the oxygen supply rate high especially during the desiliconization reaction promotion period, the desiliconization flux for injecting and the upper dephosphorization flux The desiliconization and dephosphorization effects of top-blown oxygen are maximized, and high desiliconization and dephosphorization effects can be obtained in a short period of time. Furthermore, as the treatment time is shortened, decarburization and deMn reactions are suppressed, and a drop in hot metal temperature can also be suppressed to a minimum, and many other secondary effects can also be achieved.

[Brief explanation of drawings]

FIG. 1 is a graph showing how Si and P decrease during desiliconization and dephosphorization.

Claims (1)

[Scope of Claims] 1. Hot metal that has not been substantially subjected to desiliconization treatment is charged into a pretreatment furnace, and the surface of the hot metal in the pretreatment furnace is covered with dephosphorization flux, and oxygen is top-blown and desiliconized. When desiliconizing and dephosphorizing hot metal by adding an injection of desiliconizing flux containing an oxygen source for silicon, in the desiliconizing reaction acceleration stage,
Desiliconization oxygen supply rate [V ₀ (Unit: Kg/1 ton of hot metal
A method for desiliconization and dephosphorization of hot metal, characterized in that the conditions for blowing top-blown oxygen and/or the injection conditions for desiliconization flux are adjusted so that the following equation (min)] satisfies the following equation: [V ₀ ] = η _s・O _s + η _g・O _g ≧ 2 [Si] ₀ −0.2 …[] However, [Si] ₀ : Silicon concentration in hot metal before treatment (wt%) η _g : Top-blown oxygen Desiliconizing oxygen efficiency (10 ^-2 %) 0.2≦η _g ≦0.7 η _s : Desiliconizing oxygen efficiency of desiliconizing flux (10 ^-2
%) 0.4≦η _s ≦1.0 O _g : Top-blown oxygen supply rate (Kg/t・min) O _s : Injection rate of desiliconization flux (oxygen content equivalent value: Kg/t・min)